This invention relates to a weighing apparatus using two or more load cells and more particularly to such an apparatus having an improved arrangement for reducing the need for load shift adjustment.
Weighing apparatus using multiple load cells are used widely in the weighing industry for weighing loads from a few pounds to many tons. Such weighing apparatus typically includes a base, multiple load cells for producing a signal in accordance with the weight of the load applied, a weigh platter which directly receives the load, and a weigh frame which receives and transfers the load from the weigh platter to the load cells.
Load cells, particularly those employing beams, are typically designed so as to measure a force which is applied to the load cell in a single direction. Problems arise when weight is placed on the weighing apparatus so as to cause components of force to be applied to the load cell in other directions. This typically happens with off center placement of the weight on the weigh platter which give rise to moments and weighing results that vary with load position. These errors may be classified as transverse and longitudinal load position or load shift errors, depending on the placement of the load with respect to the longitudinal axis of the load cell beam. These errors need to be corrected if accurate weight readings are to be obtained.
Typically, each load cell in a weighing apparatus must be corrected for both transverse and longitudinal shift errors. Such correction is referred to as "shift adjust" and the methods of correction typically involve honing of parts of the load cells, or utilization of electrical components such as resistors or of software based mathematical correction of the weight signals. Such methods add a significant expense in parts and labor and complicate the construction of the weighing apparatus, particularly in less expensive apparatus.